Modulators, frequency changers and detectors using rectifiers with frequency-dependent characteristics

In the calculation of the performance of modulators, frequency changers, and detectors it is found difficult to allow for any frequency dependence of the resistance characteristic of the rectifier, although when copper-oxide rectifiers are used, such dependence is very severe. An approximate method of allowing for such an effect is described in the paper, and it can be applied easily to the analysis of circuits where the terminating impedances are finite only at a finite number of modulation-product frequencies and zero at all other such frequencies. In particular, the case where either the input or the output frequency is low, the carrier frequency is high and only one sideband is accepted is considered in some detail, and the results are illustrated by numerical examples based on copper-oxide modulators working at frequencies up to 6 Mc/s. It is also shown how the conversion insertion-loss can be stabilized against temperature variation by a suitable choice of terminating resistance. The working and results are the same for shunt, series and ring modulators, for conditions of low input frequency with high output frequency and vice versa.